The National Weather Service broadcasts weather and weather emergencies across the United States using seven different regional weather channels. These seven channels range in frequency from 162.4 to 162.55 MHz and employ narrow band FM modulation. When a regional weather emergency exists, the weather service modulates a 1050 Hz tone on the appropriate 162 MHz weather frequency for 10 seconds to alert the public of an impending weather emergency. However, the 1050 Hz tone will not be heard by anyone who is not listening to a radio tuned to that local weather channel at 162 MHz, at the time of the emergency.